The present invention pertains to high velocity web dryers in which a running web is floatingly suspended on air bars as it moves through the dryer. The general arrangement of this type of high velocity air web dryer and duct arrangement is shown in the U.S. Pat. No. 3,739,491 which issued June 19, 1973 to Creapo et al.
More particularly the invention pertains to means for providing heat to the interior of the dryer including a gas fired burner for heating a supply of combustion air and then delivering the heat to the interior of the web dryer. Such a general arrangement is shown in the U.S. Pat. No. 4,116,620 issued Sept. 26, 1978 to Paul H. Stibbe, and also in the U.S. Pat. No. 4,343,769 which issued Aug. 10, 1982 to Gary L. Henkelmann.
In prior art dryers of the above type, which use energy efficient burners, it is necessary to limit combustion air to a stoichiometry combustion level at all firing conditions. This is normally done with a butterfly type damper, which opens or closes as firing rate demands change. To achieve minimum firing rate and pilot flame conditions with the above type systems, the combustion air valve needed to be throttled to an almost closed position. This slightly open position created an unstable situation, with the slightest movement of throttle creating a starvation for oxygen, or an over abundance and in-rush of air which occasionally would blow the flame out.